1. Field of the Invention
The present invention relates to an optical signal transmitting apparatus, an optical data bus system and a signal processing apparatus, and more particularly to an optical signal transmitting apparatus for emitting incident optical signals in a plurally branched state, an optical data bus system using the optical signal transmitting apparatus, and a signal processing apparatus using the optical data bus system.
2. Description of the Related Art
As a result of very large scale integrated (VLSI) circuits, the range of circuit functions of daughter boards for use in a data processing system has substantially expanded. As the number of signals connected to each daughter board increases along with the increase in circuit functions, a parallel architecture requiring many connectors and connecting lines is adopted for the data bus board (mother board) for connecting the daughter boards in a bus structure. While the operating speed of the parallel bus has been enhanced by the use of multiple layers of fine connection lines in the parallel architecture, the processing speed of the system is sometimes limited by the operating speed of the parallel bus as a consequence of signal delays due to inter-wiring capacitance and the resistance of connection wiring. Also the problem of electromagnetic interference (EMI) due to the increased density of parallel bus wiring also poses a severe constraint to the enhancement of system processing speed.
In order to solve these problems and enhance the operating speed of the parallel bus, possible use of an intra-system optical connection technique known as optical interconnection is being studied. Various forms of optical interconnection, as its outlines described by Uchida, the Scientific Lecture Convention on Circuit Packaging 15C01, pp. 201-202(in Japanese) and H. Tomimuro et al, IEEE Tokyo Section Denshi Tokyo No. 33, pp. 81-86 (1994) reveal, are proposed, differing with the configuration of the system.
Of the various forms of optical interconnection technique so far proposed, an optical data transmission formula using a light emitting/receiving device is disclosed in Japanese Published Unexamined Patent Application No. Hei 2-41042. This patent application proposes a serial data bus for loop transmission among daughter boards in which light emitting/receiving devices are disposed on the top and bottom sides of each daughter board, and the light emitting/receiving device on adjoining daughter boards incorporated into a system frame are spatially coupled by light. According to this formula, an optical signal sent from any one daughter board is opto-electrically converted in an adjoining daughter board, on which the signal is further electro-optically converted to send the resultant optical signal to the next adjoining daughter board, so that the daughter boards are successively arranged in series and the signal is transmitted to every daughter board built into the system frame while repeating opto-electric and electro-optical conversions. As a result, the speed of signal transmission both depends on and is limited by the speed of opto-electric or electro-optical conversion of the light receiving/emitting device arranged on each daughter board. Furthermore, since data transmission between daughter boards uses optical coupling, in which free space intervenes, by the light receiving/emitting devices arranged on the daughter boards, interference between adjoining optical data transmission paths (cross talk) is likely to arise and invite faulty transmission of data. Faulty transmission of data may also arise from some environmental factor in the system frame, for instance the scattering of optical signals by dust or the like.
Japanese Published Unexamined Patent Application No. Sho 61-196210 proposes a formula by which daughter boards are coupled via an optical path including diffraction gratings and reflective elements arranged over the surface of a plate. According to this formula, since light emitted from one point can be connected to only one fixed point, it is impossible to comprehensively connect all the daughter boards as an electric bus does.
Also, a number of patents have been applied for regarding data transmission between daughter boards using an optical connecting device equipped with a branching element.
Japanese Published Unexamined Patent Application No. Sho 58-42333 discloses an instance of data transmission between daughter boards using plural half mirrors. However, where plural half mirrors are used, the overall hardware size tends to become large, and each mirror should be coordinated in optical position relative to the pertinent light emitting/receiving device. Moreover, since transmitted light having passed a half mirror is approximately halved in optical intensity compared with the incident light, repetition of branching and transmission more than once substantially weakens the optical intensity with the consequence that the light receiving device can obtain no sufficient light intensity and signal transmission is thereby made impossible.
Japanese Published Unexamined Patent Application No. Hei 4-134415 reveals a formula by which an optical signal is brought to incidence on a side of lens array in which plural lenses are formed and each lens emits the signal. According to this formula, the closer a lens is to the incident position of light, the greater the luminous energy emitted from the lens, and this may result in intensity fluctuations of the emitted signal depending on the positional relationship between incidence and emission. Furthermore, the utilization efficiency of the incident luminous energy is low because a considerable proportion of the light coming incidence from one side escapes from the opposite side.
There is also an optical bus formula using an optical fiber, as disclosed in Japanese Published Unexamined Patent Application No. Sho 63-1223, by which substantially uniform optical signals can be transmitted by successively increasing the ratio of branching from the input end onward. A method for forming a coupler adaptable to such a formula is described in the IEEE Photonics Technology Letters, Vol. 8, No. 12, December (1996)p1650. The coupler forming method described therein achieves branching with a V groove formed in the optical fiber. Conceivably, by adjusting the size of the V groove, the output luminous energy may be adjusted, but it is extremely difficult to produce such an arrangement, and utilization of the incident luminous efficiency would be inadequate, too.
Further, a star coupler for uniformizing the intensities of branched optical signals is disclosed in the Japanese Published Unexamined Patent Application No. Hei 9-184941. This star coupler schematically has plural optical fibers of which the ends on one side are bundled and fixed, and an optical waveguide large enough to cover the plural optical fibers brought into contact with one end face of the bundle, of which the other end face is provided with an optical reflector.
Where such a coupler is used for data transmission between daughter boards, an increase in the number of boards would result in a corresponding increase in the number of the fibers to be connected to a light receiving/emitting element, inviting a greater complexity of configuration and a consequent larger size of hardware.
The present invention, attempted in view of the above-described circumstances, is intended to provide an optical signal transmitting apparatus permitting easy laying out of connecting boards, an optical data bus system using more than one such optical signal transmitting apparatus, and a signal processing apparatus using that optical data bus to carry out signal processing including transmission and reception of data.
To achieve this intention, according to the invention, there are provided a light transmitting medium having plural level gaps at one end of the light transmitting medium, in which the plural level gaps correspond to plural incidence/emission portion and an optical signal is incident on and/or emitted from the plural incidence/emission portions, and a reflector arranged at the other end of the light transmitting medium which reflects the optical signal being incident from the incidence/emission portion toward the plural the incidence/emission portions.
Thus, by disposing plural level gaps at one end of the light transmitting medium, plural level gaps are corresponded to the incidence/emission portions. Preferably, the incidence/emission portions are formed by disposing stepwise plural level gaps at one end of the light transmitting medium. At the other end of the light transmitting medium, the reflector is provided to reflect optical signal being incident from the incidence/emission portion toward the plural the incidence/emission portions.
Therefore, if an optical signal is incident through one of the plural the incidence/emission portions, the optical signal is transmitted through the light transmitting medium and reaches the reflector. The optical signal having reached the reflector is reflected toward the incidence/emission portion.
Thus, as the light transmitting medium is so that the incidence/emission portions have level gaps, where light emission/receiving element is to be arranged to face the incidence/emission portion, if the light emission/receiving element is provided on a daughter board, the daughter boards can be installed side by side, resulting in a simplified layout.
It is desirable to configure a side of the light transmitting medium to reflect part of the optical signal so as to guide to the incidence/emission portions, because the utilization efficiency of light can be enhanced.
The length of each of the plural level gaps formed on one end of the light transmitting medium here may as well be made equal to the others. Or else the light transmitting medium may be provided with the plural level gaps so as to satisfy the condition of L2xe2x89xa7L1, where L1 is the length of each of the plural level gaps and L2 is the distance from the other end of the light transmitting medium to the incidence/emission portions positioned closest to that other end.
Also, the incidence/emission portions of the light transmitting medium may reflect the incident optical signals toward the reflector and reflect the optical signals reflected by the reflector and by the side in the direction reverse to the direction of incidence. Thus, the surfaces of the light transmitting medium serving as the incidence/emission portions are formed to constitute 45xc2x0 angles to the upper surface of the light transmitting medium. In this case, ideally, the surfaces constituting the incidence/emission portions should be totally reflective surfaces. And at least one of the plural incidence/emission portions may reflect optical signals in a direction difference from the reflective directions of the other incidence/emission portions.
Alternatively, the side surfaces of the light transmitting medium may as well guide the rest part of the optical signal except the part of the optical signal directly reflected to the incidence/emission portion so as to guide to the whole incidence/emission portions. Thus the utilization efficiency of light can be enhanced.
For instance, the light transmitting medium may as well be configured so as to establish the relationship of tan xcex8xe2x89xa7tan 3xcex8xe2x80x2, where 2xcex8 is the diffusion angle of an diffuser and 2xcex8xe2x80x2 is the maximum angle of vision from the optical diffuser toward the closest incidence/emission portion. The light transmitting medium may also be configured so as to establish the relationship of xcex8xe2x89xa6xcfx86 where 2xcex8 is the diffusion angle of the diffuser and sin xcfx86 is the numerical aperture of the light transmitting medium.
The reflector may either diffusively reflect the optical signal or performs mirror reflection.
It is also possible, using the optical signal transmitting apparatus according to the invention to provide an optical data bus system for transmitting data by way of optical signals.
Here is further proposed a signal processing apparatus provided with an optical signal transmitting apparatus, and an circuit board including a light emitting/receiving element which is disposed to face the incidence/emission portion and transmits and/or detects the optical signal. Thus, when an optical signal is brought to incidence on an incidence/emission portion, it is branched as described above, and emitted externally via the plural incidence/emission portions. The light receiving elements receive optical signals emitted from the plural incidence/emission portions.
Further, a signal processing circuit according to the invention has: a first optical signal transmitting apparatus in which plural incidence/emission portions for the incidence/emission of an optical signal are formed stepwise; a second optical signal transmitting apparatus in which plural incidence/emission portions for the incidence/emission of an optical signal are formed stepwise, or, a supporting board that supports the first optical signal transmitting apparatus and is equipped with plural connectors; plural daughter boards each having a first emission/receiving element disposed to face the incidence/emission portion of the first optical signal transmitting apparatus; and a second emission/receiving element disposed to face the incidence/emission portion of the second optical signal transmitting apparatus, or, a receptive connector to be connected to the connectors. The interval between the first emission/receiving element and the second emission/receiving element or the receptive connectors of the plural daughter boards are set substantially the same, and the plural daughter boards are fitted upright relative to the first optical signal transmitting apparatus. The plural daughter boards are arranged side by side over the first optical signal transmitting apparatus, substantially orthogonal to a line segment connecting the plural incidence/emission portions of the first optical signal transmitting apparatus.
This enables plural boards, for which the spacing between two emission/receiving elements or the spacing between one emission/receiving element and, for instance, a connector for electric signals, is set in common, to be arranged side by side by installing the boards substantially orthogonal to a line segment connecting the plural incidence/emission portions when the boards are installed to the optical signal transmitting apparatus.